Unipolar Pulse Width Modulation Inverter
By
Randy Baggao & Gabriel Tam
Senior Project
ELECTRICAL ENGINEERING DEPARTMENT
California Polytechnic State University
San Luis Obispo
2013
Table of Contents
Section
Abstract……………………………………………………………………………………............ 4
Acknowledgements……………………………………………………………………………….. 5
I.
Introduction……………………………………………………………………………….. 6
II.
Background……………………………………………………………………………….. 8
III.
Requirements & Specification...………………………………………………………… 11
IV.
Design…………………………………………………………………………….............14
A. Control Unit………………….………………………….………………………………. 14
B. Firing Circuit……………………………………………………………………………. 18
C. H-Bridge………………………………………………………………………………… 22
V.
Testing & Results………………………………………………………………………...25
A. Control Unit………………………………………………………………………………25
B. Firing Circuit……………………………………………………………………………...30
C. H-Bridge…………………………………………………………………………………. 35
VI.
Conclusion & Recommendations………………………………………………………...39
Appendices
A.
Datasheets………………………………………………………………………………...41
B.
Gantt Chart………………………………………………………………………………. 47
C.
Parts List, Costs, and Time Schedule Allocation………………………………………...48
D.
References……………………………………………………………………………….. 50
-1-
Page Locations of Tables, Figures, & Schematics
List of Tables
Table 3-1: Unipolar and Switching PWM Logic…………………………….……….................. 12
Table 3-2: Summary of PWM Inverter Functional Description………………………................ 13
Table 3-3: Requirement Specifications of the PWM Inverter for testing…………………..…… 13
List of Figures
Figure 2-1: A Commercial Tripp-Lite Power Inverter for Mobile Vehicles………………..……. 8
Figure 2-2: Photovoltaic Grid System Left-Installation Right- Photo of Solar Panels
installed on a School Gym…………………………………………………….................. 9
Figure 3-1: Block Diagram of the Pulse Width Modulation Inverter…………….….…...............12
Figure 3-2: Full Bridge Circuit Topology of the PWM Inverter Source Indication……...............12
Figure 5-1: PWM Inverter Wired for testing……………………………………………………..25
Figure 5-2: Filtered Triangle Output…………………………………………….….………….. 26
Figure 5-3: Output Control Voltages , and , with respect to
-12V reference and Vcont = 0 (ie. = 0)…………………………………….…………27
Figure 5-4: and - with respect to proto board common………………….………... 28
Figure 5-5: Output Control Voltage V(A+, A-) on top and V(B+, B-) on bottom with respect
to -12V, where positive……………………………….........................................29
Figure 5-6: Control Voltage V(A+, A-) on top and V(B+, B-) on bottom with respect
to -12V, where negative………………………………………………................. 29
Figure 5-7: Idealized VLOAD at Overmodulation Region………………………………............... 30
Figure 5-8: V(A+,A-) on top and Optocoupler A+ output on bottom…………………............... 32
-2-
Figure 5-9: V(A+, A-) on top and Optocoupler A- output on bottom…………………............... 32
Figure 5-10: Optocoupler Outputs A+ (top) and A- (bottom)……………………………………33
Figure 5-11: V(A+, A-) on top and Driver A+ on bottom………………………………………. 34
Figure 5-12: V(A+, A-) on top and Driver A- on bottom……………………………..………… 34
Figure 5-13: Driver A+ on top and Driver A- on bottom………………………...………………35
Figure 5-14: MOSFET A+ on top and MOSFET A- on bottom……………………....................36
Figure 5-15: MOSFET B+ on top and MOSFET B- on bottom………………………………… 36
Figure 5-16: Unfiltered AC Voltage Output…………………………………………………….. 37
Figure 5-17: Filtered AC Voltage Output……………………………………………………….. 38
Figure 5-18: Final Product of Unipolar PWM Inverter…………………………………………. 38
List of Schematics
Schematic 4-1: PWM Inverter Control Circuit………………………………………………….. 17
Schematic 4-2: Isolated Firing Circuit with Optocoupler and Gate Drivers……………………..20
Schematic 4-3: Terminal Connections for all 4 Firing Circuits…………………….……………21
Schematic 4-4: H-Bridge of the Inverter………………………………………………………....23
Schematic 4-5: Physical Layout of Inverter…………………………………………………….. 24
-3-
Abstract
This project portrays the design and construction of a pulse width modulation (PWM) inverter.
The inverter is implemented as a unipolar converter. The inverter provides a steady single-phase
sinusoidal 60Hz AC voltage output from a DC input. This is a basic DC-AC power converter
that is built in 3 separate phases and integrated altogether at the end. The inverter can be broken
down into the control unit, firing circuit, and the H-bridge. By using the PWM method, one can
control the frequency and amplitude of the output by using a reference signal. This method will
also avoid using a transformer because transformers have high power losses. This project will be
dedicated to EE-410 power electronics students as an experiment to observe and experience the
fundamental operations of a PWM inverter circuit at Cal Poly.
-4-
Acknowledgments
We would like to express thanks to Jaime Carmo, the Electrical Engineering
Department’s Electronic Technician, for devoting his time to the faculty and students and
especially for helping create a case for our senior project. We would also like to express thanks
to our project advisors Taufik and Ahmad Nafisi for teaching us the concepts of Electrical
Engineering through our college careers and also guiding us through these last few quarters to
making a successful working product.
-5-
I.
Introduction
Power Engineering has seen a rapid growth in efficient energy solutions. Power
electronics focuses on processing electrical power using electronics with high efficiency and less
power loss. Power electronics is found in applications of modified electrical energy. Some
examples include low voltage cellular devices and high voltage transmission lines. Efficiency
plays a large role in power electronics whereas inefficient systems are impractical and result in
wasted energy and higher costs in utilities or reliability of components.
Some types of efficient source conversions include AC-to-AC, DC-to-DC, AC-to-DC,
and DC-to-AC source conversions. AC-to-DC converters are best known as rectifiers while DCto-AC converters are known as inverters [1]. Today’s popular power conversion type includes
the use of photovoltaic (PV) solar panels to take in DC Power and convert it to supply household
AC power sources. Computers, cell phones, televisions, microwaves, etc. have been sourced by
AC power through some sort of energy conversion which will allow these appliances to function
without “blowing up” on startup. With the conversion of AC-to-DC sources, a solution of using
house hold appliances on the go took place that lead to the use of power inverters. This allowed
the reverse conversion of DC-to-AC inverter power supply sources giving designers and
customers the option of using larger scale DC batteries to power household appliances at any
specified voltage rating.
It is important for electrical engineering students who are focusing on power electronic
conversions, to learn the basics on inverter circuits as it is one of the four major conversion
types. At Cal Poly, the course that covers the foundation of the four basic conversion processes is
EE410: Introduction to Power Electronics. The course has a lab portion where students get the
hands-on experience on several basic power converters. Currently however, the lab lacks one
-6-
important experiment in which students can learn the operation and performance of an inverter
circuit. This senior design project aims to develop an inverter circuit experiment which addresses
several concepts and techniques used in covering DC to AC inverters.
-7-
II. Background
DC-to-AC inverters are seeing a rapid growth in contributing renewable energy sources.
An example of a DC-to-AC inverter application may include uninterruptible power supplies
known as backup generators that supply power from the use of batteries (DC source) and invert it
(previously converted and stored again as a DC power) into AC power [9]. A simpler way to
understand inverters is the application of converting DC power into AC power using a
commercially available car inverter that is used for car electrical outlets to allow household
electronics to be used by a car battery source as seen in Figure 2-1.
Figure 2-1: A Commercial Tripp-Lite Power Inverter for Mobile Vehicles [12]
In air conditioning, an inverter can adjust the input frequency to control the speed of its
motor. The desired room temperature is achieved by adjusting the output frequency of the
inverting control unit. There are many types of control units that may be selected according to
the designers preferred choice of specifications that will make the product run efficiently and
with lower cost [3].
-8-
Inverters play an important role in Power Electronics as it applies to larger device
applications that help change the development of electronic machinery. The increase use of
inverters are due to increasing use of grid tied residential PV. Figure 2-2 shows how a
photovoltaic grid system is installed.
Figure 2-2: Photovoltaic Grid System Left-Installation Right-Photo of Solar Panels installed on a School Gym [10][11].
The power electronic classes provided by California Polytechnic State University help
prepare students in the power industry. There are currently four power electronics courses
offered as technical elective courses for electrical engineering majors. The four courses are
EE410 (Power Electronics I), EE411 (Power Electronics II), EE433 (Introduction to Magnetic
Design), and EE527 (Advanced Topics in Power Electronics). Many lab experiments include
concepts of rectification using single and three phase source inputs, non-isolated converters like
buck and boost as well as isolated converters such as a fly-back circuit, magnetic design and
various computer simulation exercises [1], [2]. The labs provide little hands-on experience to
concepts explained in lecture which sometimes are further explored in computer simulation.
Some of the experiments created are provided by students that have had the privileges to taking
these classes and have their senior projects to help improve the experience in the power
electronics labs.
-9-
This senior project is an example of such an effort. More specifically, this senior project
has the objective to improve a previous effort by another senior project team to design and
develop a lab experiment in switching PWM inverter [5]. The following chapter details the many
aspects this senior project will improve.
- 10 -
III. Requirements & Specifications
The project consists of the design and development of a PWM inverter that amplifies a
small input signal Vcont and outputting voltages +VDC, –VDC or 0 at the load depending on how
+VCont or -VCont compares to the reference triangle waveform VTri. VCont is provided by an AC
Wall Wart that produces 4.5VRMS at a steady 60Hz frequency and adjustable by a trimmer knob
of up to 500Ω. One of the op-amps to the TLE2072CP componen of the control unit uses an
inverting amplifier to invert the VCont signal and produce –VCont.
The inputs VDC are from isolated rail DC voltages at +12V and -12V, provided by
multiple DC-DC converter chips that are supplied from a DC power supply. The waveform
generator chip outputs 22kHz triangle-wave VTri after it is powered by the rail voltages. The
LM339AN comparator chip performs the PWM logic comparison and is also powered by the
control circuit’s isolated rail voltage. The output load voltage is similar to VCont but contains
harmonics centered at even multiples between the ratio of the triangular waveform frequency fTri
and the continuous waveform fCont which is also known as frequency modulation mf.
The three circuits (Control, Firing and H-bridge circuits) are built onto a single proto
circuit board. Each circuit is isolated from one another by using DC-to-DC converter chips and
isolated grounds. This allows easy testing and troubleshooting at each different circuit. The
physical area of the board is about 5”x7”x2”. After extensive testing, the circuit will be encased
in plexiglass about 8”x10”x5”.
The circuit will be powered by a DC Power Supply to power the control and firing
circuit, a DC wall wart to provide the input of the inversion, and an AC wall wart to create the
continuous sinusoidal waveform. The output that is monitored is an AC sinusoidal signal based
on the amplitude modulation ma which is the ratio of VCont and VTri controlled by a trimmer knob
- 11 -
to set the output to be either linear overmodulation, or saturation. The second output is the
unfiltered AC output to confirm unipolar measurements of V+ to 0 or V- to 0.
Figure 3-1: Block diagram of the Pulse Width Modulation Inverter.
Figure 3-2: Full Bridge Circuit Topology of the PWM inverter Source Indications [1]
Table 3-1: Unipolar Switching PWM Logic [1] [4]
Switches [On]
S1
S2
S3
S4
Unipolar Switching Logarithm
0
! " !
! " 0
- 12 -
Table 3-2: Summary of PWM Inverter Functional Description
Module
Inputs
Outputs
Functionality
Unipolar PWM Inverter
DC Input: +/-12 V DC Rail from Power Supply supplies the entire circuit
PWM Control Input: Produces the Characteristic Waveform to be modulated by the
chip within a grand scale switching frequency range from 10kHz to 25kHz. Test data
should show similar results when an input triangular waveform is compared with a
sinusoidal input controlled waveform.
AC Output: Should produce a 60Hz constant output signal from the inverting DC-toAC device. The DC power is held by the DC-to-DC chip which will readily be
modified through the inverting chip. The output waveform should follow a unipolar
PWM waveform.
The Pulse Width Modulation Inverter will take a +/-12V DC input and compare a
controlled sinusoidal waveform with an input triangular waveform to produce a PWM
output inverter.
Table 3-3: Requirement Specifications of the PWM Inverter for testing
Marketing
Requirements
2,5
1,3,4
1,4,5
3,4
Engineering Requirements
1. Total Harmonic Distortion of PWM
should be < 5-10%
2. System must be compact, portable,
and safer to use compared to older
version.
3. System should be able to work as
inverter: 20-40 V DC input source Variable AC Output
4. The system must be built on PCB
board with no extra materials i.e.
wood, plastic.
Justification
The high-speed amplifiers can
easily achieve this kind of THD.
No complicated steps necessary
to turn on the product and should
be safe for the customer.
Standard Inverter conversion of
DC to AC wall warts.
Compared to the previous
version, the circuit board was
held together with a block of
wood. Simplify connections and
use only electrical boards.
Marketing Requirements
1. Should be easy to use.
2. Should use PWM.
3. Should have 3 parts: firing, control, inverter circuits.
4. Should be simplified and portable.
5. Should be able to get desired an adjustable AC Voltage at a steady 60 Hz Output.
- 13 -
IV. Design
Control Unit
The control unit of the inverter is used to produce firing signals to the four MOSFETs in
the H-bridge. Schematic 4-1 displays the schematic of the control unit. The DC power supply
will provide + #$ % to the DC-DC converter to transmit isolated & #$ % to the waveform
generator, op-amp, and comparator. The waveform generator will provide a triangle waveform at
pin 3. The frequency of the triangle output waveform can be controlled by a timing capacitor at
pin 10. The 500Ω trimmer will determine the rise time and fall time of the triangle waveform.
There is a high-pass filter to allow only DC signal of the triangle wave to go through. The
inverting op-amp inverts the small AC signal to the negative AC signal ! . The AC
signal, , can be used to amplify the amplitude of ( at the output with the 500Ω
potentiometer. The 1kΩ trimmer can be adjusted to vary the amplitude of ! to sync with
. The comparator will be used to perform the PWM logic by comparing the triangle and
sine wave to create pulses that will send current to the optocouplers to switch them on and off
accordingly. The comparator will send pulses to the firing circuits of ( , ( that controls
MOSFETs ( & ( and * , * that controls MOSFETs * & * [6].
- 14 -
Specifications
• Input: +12Vdc regulated from 2W DC converter chip
• Reference: -12Vdc regulated from 2W DC converter chip
• Vcontrol = 60Hz, 4.5Vrms AC signal and 500Ω potentiometer
• Protoboard common connected to 0V output pin 2W, DC converter chip
Waveform Generator – Model NTE864
Ratings: 15mA max
Min: 10V
Max: 30V
Trimmer (500Ω) – Pins 4 & 5
• Vsupply = Vd = 12V
• Need: ~6
./0
•
-
•
Two Resistors (1kΩ each) will be in series with trimmer.
12
20004
Timing Capacitor – Pin 10
• According to datasheet: Ra = Rb = 1.5kΩ
• Vd = 12V
• Need: Operating Frequency = 22kHz
./0
•
5 •
•
•
Need: Fairly large capacitor.
Ideal capacitor = 0.01uF
Actual size: 16nF
..678
8
Inverting Op Amp – Model TLE2072CP
Ratings: Supply 3.1mA
Output: 20mA
Voltage Supply: 2.25V ~ 19V
- 15 -
Trimmer (1kΩ) – Pin 2
• Standard Range: 10Ω to 1MΩ
• Used: 9.53kΩ to output 6mA
•
:;
Max Variable Gain = :< :/
:.
=
=.6;78
.78
Comparator – Model LM339 Quad
Ratings: 2V~ 36 5ABCD -EAFG
Current Max: 18mA
Vd = 12V
Vgnd = -12V reference
- 16 -
9.53
Schematic 4-1: PWM Inverter Control
Circuit
+12Vdc regulated from
2W, DC-DC converter
V(A+, A-)
V(B+,B-)
Vcc-
1.5kΩ, 1/2 W
DC - DC
+12V
from
DC
power
1 2
4 5 6
1.5kΩ, 1/2 W
High-pass filter
to block DC
Filtered and
buffered triangle
wave
0.01uF
270kΩ
100kΩ
16nF (Freq. Control)
1kΩ
14
8
Waveform Generator
8
5
OP AMP
1
1
4
7
14
8
COMPARATOR
1
7
10kΩ
270kΩ
1kΩ
..
1kΩ
9.53kΩ
22kHz triangle
wave
500Ω Trimmer
1kΩ
-Vcont
Vcont
-12Vdc regulated from
2W, DC-DC converter
Refer to Appendix for IC pin
configurations
1kΩ Trimmer
500Ω Potentiometer
Proto board common
ground, 0V
17
60 Hz, 4.5Vrms signal
from function
generator
Firing Circuit
There are four separate firing circuits that are used to drive the inverting and noninverting chips with pulses from ( , ( and * , * accordingly. The schematic of the
full firing circuit is displayed in Schematic 4-2. The isolated DC-DC converters will be used to
power the chips with H⁄! #$ % and isolate the firing circuit from the control unit and Hbridge. Each individual firing circuit will need an optocoupler, an inverting or non-inverting
driver chip, a switching diode, and separate passive resistors and capacitors. The optocoupler
will electrically isolate the PWM controller outputs from the gate terminal of the power
MOSFET, so then the source terminal of the power MOSFET has a “floating” ground. The
optocouplers have to be isolated from the PWM control circuit because the source terminal of the
respective MOSFET must be connected to its local ground reference. It also isolates the higher
voltage on the high power side of the H-bridge from the control circuit to prevent ICs from being
damaged and noise turbulences. Schematic 4-3 displays 4 firing circuits that are connected
similarly to one another [7].
18
Specifications
• Output of the control unit goes into the input of the optocoupler
• Input: +12V that is isolated from PWM circuit
• Reference: DC converter chip
Optocoupler – Model Vishay 6N136
Ratings: Supply: -0.5V to 15V
Output: -0.5V to 15V
Max output current: 8mA to 16mA
Pins 6 & 8
Want: I 1.19mA
./N
I .OPΩ R 1.2mA
MOSFET Driver – Model TC1426(Inverting) & TC1427(Non-Inverting)
Ratings: Supply: +18V
Range: 4.5V to 16V
Output Current Peak: 1.2A
Power Dissipation: 730mW
Diode Snubber Circuit
• Fast Switching Diode: 75V, 150mA
• Small Resistance for Diode R10Ω
• Parallel Resistance R 1kΩ
19
One firing circuit for each MOSFET.
Switches A- and B- share a power supply
and ground. However, A+ and B+ must use
separate power supplies and grounds. Do
not connect any of these grounds to the
ground of the control circuit.
MOSFET
G
D
Schematic 4-2: Isolated Firing
Circuit with Optocoupler and
Gate Drivers
S
100kΩ
Grounds (isolated
from control
circuit)
Switching diode
0.1uF
1.2kΩ
10Ω
5
Switches A+ and B+
use inverting drivers.
4
Inverting Driver
8
1
5
4
Green for A+, B+
Black for A-, B-
Optocoupler
+12V isolated
from the PWM
control circuit
10Ω
8
Connects to
Control Circuit
1
O+
DC - DC, 1W
1
2
3
4
DC - DC, 2W
1
2
4
Switches A- and Buse non-inverting
drivers.
5
6
20
O-
Vcc+ and GND
supplied by DC
power supply shares
nodes with A- and B-
A+
A-
Firing Circuit
+
-
B+
Firing Circuit
+
-
B-
Firing Circuit
+
-
Firing Circuit
+
-
-12V
reference
V(A+,A-) V(B+,B-)
DC Supply
Control Circuit
AC Control
Schematic 4-3: Terminal connections for all 4 firing circuits
21
H-Bridge
The H-bridge of the inverter circuit can be shown in Schematic 4-4 and the layout
consisting of all three circuits can be seen in Schematic 4-5. There are 4 separate power
MOSFETs that are used to perform the switching in the H-bridge. Unipolar switching will
require all 4 switches in order to have the output of the inverter to be switched from H to 0 or
from ! to 0. An electrolytic capacitor is placed across the positive and negative terminals of
the H input as a filter to provide current ripple into the inverter so the DC current will have
fewer ripples. Two fuses are placed across the H input as safety to protect , and
, respectively. One fuse feeds the , side of the inverter and the other fuse feeds
the , side. An inductor and a capacitor are used as a tank circuit to decrease the damping
waveform at the output to filter the pulses for . The inductor placed to prevent the output
from shorting with the electrolytic capacitor at higher frequencies [8].
Specifications
Convert 20-40VDC power to 60Hz VAC
Low Pass Filter
f = 60Hz
TU 2VW 376.99 YEZ/\
L = 100uH
C = 10uF
1
1
15.915dbe
W] 2V√_`
2Va100Cb10Cc
22
+
Vdc
_
+
Vac
_
G
D
A+
S
G
D
S
G
D
B+
A-
Schematic 4-4: H-Bridge of the Inverter
23
S
G
D
B-
S
H-Bridge and Filters
+
+
Vdc
Vac
-
Individual heat sink
for each MOSFET.
HEAT SINKS
MUST NOT
TOUCH EACH
OTHER BECAUSE
THEY WILL
HAVE DIFFERENT
DRAIN
POTENTIALS
-
+
MOSFET
MOSFET
MOSFET
MOSFET
A+
A-
B+
B-
Firing
A+
Firing
A-
Firing
B+
Firing
B-
-
+
-
+
-
+
-
-12V
reference
V(A+, A-) V(B+,B-)
DC Supply
Control Circuit
AC Control
Schematic 4-5: Physical Layout of Inverter
24
V. Testing
Figure 5-1: PWM Inverter Wired for testing
Figure 5-1 shows the inverter wired up for testing. The H-bridge, firing circuit and
control circuit work together to invert the DC input signal into an AC output signal. In this
section, each of the three circuits are tested individually to achieve the necessary inversion.
Control Unit
Step 1
The objective of the control unit is to have the waveform generator produce a triangle wave that
will produce a clean signal with 7.8f
7f
7 by supplying the oscillator with +12V. The
triangle wave should have a frequency of approximately 22kHz with minimized DC offset by
adjusting the values of the frequency control of the waveform generator. The fall and rise time of
the triangle wave should be equal by adjusting the 500Ω trimmer to get a duty cycle set to 50%.
Figure 5-1 below displays a high-pass filtered triangle wave with minimized DC offset.
25
i
7 R 7.8
W R 22dbe
Figure 5-2: Filtered Triangle Output
Step 2
Before powering AC with 4.5:h , energize the circuit with the DC power supply and
measure the terminals across , and , with respect to -12V reference and
confirm that both waveforms are varying sharply from +24V to 0V with a 50% duty cycle.
Figure 5-3 below displays the output control voltages , and , with = 0.
26
H, !
R 12Zm
H, !
R 12Zm
Figure 5-3: Output Control Voltages ( , ( and * , * with respect to -12V reference and Vcont = 0 (ie. jk = 0).
Power up the AC to 4.5:h and raise the 500Ω potentiometer for maximum . The
operational amplifier is an inverting amplifier that will invert to - that will be used
to determine the switching in the firing circuit and H-bridge. Probe and - with
respect to proto board common. The sinusoidal waveforms should be 180ᵒ out of phase of each
other as shown in Figure 5-4. Use the 1kΩ trimmer to adjust - to make it the same RMS
magnitude as . The AC voltage with E= maximum across l , - , ]
should be approximately 21VAC.
27
Figure 5-4: and - with respect to proto board common.
Lower the 500Ω potentiometer for minimum . Use the oscilloscope to make probe
connections at , and , with respect to the -12V reference point. Gradually
increase the 500Ω potentiometer so that increases from 0V to 3VRMS. Figures 5-5
and 5-6 display the output control voltages where is positive and where is negative.
The “ON” period of one waveform gets wider whereas the other waveform gets narrower, and
it’s vice-versa for the “OFF” period. These waveforms display pulses that were created by the
comparator. The comparator in the control unit compares the triangle wave and the sine wave,
and the output is switched from +VDC to 0 or from -VDC to 0.
28
Figure 5-5: Output Control Voltage V(A+, A-) on top and V(B+, B-) on bottom with respect to -12V, where positive.
Figure 5-6: Control Voltage V(A+, A-) on top and V(B+, B-) on bottom with respect to -12V, where negative.
29
Figure 5-7 shows an oscilloscope capture of V(A+, A-) with reference to V(B+, B-) and the
“split” portion in both half cycles. If the split cycles are not the same, then adjust the gain of
! with the 1kΩ trimmer. There is a lot of noise at the output because of long vulnerable
wires.
Figure 5-7: Idealized VLOAD at overmodulation region
Firing Circuit
Step 1
Before moving onto the firing circuit, perform power supply wiring continuity checks to confirm
that:
•
The PWM control unit is isolated from the ground terminal of the DC power supply.
•
The 12V rail and ground terminal of the DC power supply is isolated from the +12V rail
and ground of the A+ firing circuit board.
30
•
The 12V rail and ground terminal of the DC power supply is connected to the +12V rail
and ground of the A- firing circuit board.
•
The H⁄! 12 and ground rails of A+ and A- are isolated to each other.
Perform the DC converter chip test by powering up the 12V supply. Check the voltage rails of
the DC converter and make sure they output +12V and -12V. If the voltage drops more than
0.5V from your nominal voltage, then you most likely have two wires shorting each other in the
circuit. If so, fix the problem before moving on or else it would cause the converter chip to fail
and break.
Step 2
Perform checks on the isolated A+ and A- firing circuits by disconnecting AC Vcont so that ma=0.
Connect oscilloscope probe 1 to V(A+, A-) from the control unit and the ground with respect to
the -12V reference. Also, connect oscilloscope probe 2 to the output of Opto A+ and the ground
lead to the common ground of the firing circuit. It is okay to connect to any ground terminals on
the firing circuit because the two signals are already isolated from each other. Figure 5-8 displays
the result.
31
H, !
Zm R 1.7
Opto A+ Output
Zm R 5.8
Figure 5-8: V(A+,A-) on top and Optocoupler A+ output on bottom
Connect oscilloscope probe 2 and its ground terminal to the Optocoupler A- output to view the
same waveforms as above. The result is shown in Figure 5-9.
H, !
Zm R 1.7
Opto A- Output
Zm R 6.3
Figure 5-9: V(A+, A-) on top and Optocoupler A- output on bottom
32
Connect probe 1 and its ground lead to the output of Optocoupler A+, and connect probe 2 and
its ground lead to the output of Optocoupler A-. The waveforms are expected to be similar as
Figure 5-10 below.
Figure 5-10: Optocoupler Outputs A+ (top) and A- (bottom)
Connect probe 1 and its ground lead to V(A+, A-) with respect to -12V reference. Connect probe
2 and its ground lead to the output of Driver A+. Figure 5-11 displays the correct waveform of
the output.
33
H, !
Driver A+ Output
Zm R 5.6
Figure 5-11: V(A+, A-) on top and Driver A+ on bottom
Connect probe 2 to the output of Driver A+. Figure 5-12 displays the correct waveform of the
output. It will be an inverting waveform because the driver receives inverting pulses from the
control unit.
H, !
Driver A- Output
Zm R 6.7
Figure 5-12: V(A+, A-) on top and Driver A- on bottom
34
Connect probe 1 and its ground lead to the output of Driver A+. Leave probe 2 and its ground
lead to the output of Driver A-. The two waveforms should be opposite of each other because
one is inverting whereas the other isn’t. There should not be any visible overlap in “on” times
because with ma = 0, their duty cycles should be close to 50%. This is illustrated in Figure 5-13.
Figure 5-13: Driver A+ on top and Driver A- on bottom
Step 3
Repeat step 2 for firing circuits B+ and B-. The waveforms of firing circuits B will be exactly the
same as the waveforms in firing circuits A.
After finishing firing circuits B+ and B-, disconnect both the DC supply and AC Vcont.
H-Bridge
Step 1
To test the H-bridge of the inverter, confirm that firing circuits A+ is isolated from A- and B+ is
isolated from B-. Energize the firing circuit with the DC power supply, but leave AC Vcont off.
35
Attach oscilloscope probe 1 and its ground lead across VGS of MOSFET A+, and attach
oscilloscope probe 2 and its ground lead across VGS of MOSFET A-. The waveforms should
appear as shown in Figure 5-14.
MOSFET A+
n R 4.5Zm
MOSFET An R 4.5Zm
Figure 5-14: MOSFET A+ on top and MOSFET A- on bottom
Repeat the previous steps for B+ and B- to attain the waveform as shown in Figure 5-15.
MOSFET B+
n R 4.5Zm
MOSFET Bn R 4.5Zm
Figure 5-15: MOSFET B+ on top and MOSFET B- on bottom
36
Step 2
Test the inverter by inputting a 20VDC into the H-bridge and it will output an AC voltage of
approximately 142o . nominal at 60Hz at maximum . The Figures of 5-16 and 5-17
shows the waveforms of the unfiltered AC voltage output and filtered AC voltage output. By
varying the 500Ω potentiometer, the can increase or decrease the magnitude of the output
AC voltage.
Figure 5-16: Unfiltered AC Voltage Output
37
Figure 5-17: Filtered AC Voltage Output
The final product of the unipolar PWM inverter can be seen in Figure 5-18.
Figure 5-18: Final Product of Unipolar PWM Inverter
38
VI. Conclusion & Improvements
The PWM inverter was built to be a prototype in the laboratory for EE-410. This project
was created into three sections: the control unit, firing circuit, and the H-bridge, which were all
integrated to invert DC voltage into AC voltage and uses unipolar switching. The project was
most practical for unipolar switching because the inverter utilizes the right number of
components and more efficient for it.
The inverter produced a clean AC output waveform that proves that the circuit works
successfully. The circuit produced a steady 60Hz amplitude varying AC voltage at the output.
The inverter was tested to only handle up to 50Vdc because anything higher than that caused the
filter capacitors to explode. Future EE-410 students could utilize unipolar switching without any
problems.
The problems encountered that slowed the pace of our project were the wires and faulty
chip components. Even though troubleshooting was not a big problem, the wires were the main
cause for noise in our circuit. The comparator was our only component problem because it would
breakdown easily if signals going in and out were corrupted. This was fixed by finding the most
updated component that performs similar or even better than the previous component.
The improvements made in comparison to the previous design include using a waveform
generator chip NTE864 to output a triangle waveform which cuts the need of using multiple
function generators in the lab. Another improvement made to the previous design was to use a
single input for the 12V DC side to supply both the control circuit and the firing circuit which
cuts the need for extra power supplies. One last improvement made to the design was to build
39
the circuit onto one circuit board which includes a low voltage circuit side and a high voltage
circuit side and also cover the board with a protective visible case.
Future improvement for this project would be to use a pre-made printed circuit board
(PCB) so that components could be soldered on without having wires. This would be the most
efficient way to have a cleaner and less expensive project. Even though soldering took a long
time, it was the best way to troubleshoot for any errors that had occurred. Another improvement
to consider in the design would be to use a controllable Boost Converter instead of using a DC
wall wart to power the switches in the H-Bridge. This would eliminate the need for another piece
of equipment by stepping up 12V power from the control and firing circuits’ supply sources and
with user control, vary the input source of the H-Bridge while keeping the output the same.
40
Appendix A: Datasheets
Pin #
1
2
4
5
6
Function
+Vin
GND
-V
0V
+V
Murata Power Solutions NMH Series 2 Watt DC-DC Converter [15]
41
Murata Power Solutions NKE Series 1 Watt Isolated DC-DC Converter [18]
42
Pin #
Symbol
I/O Type
Function
1
SA1
I
Adjust Sine Waveform Input 1
2
SWO
O
Sine Wave Output
3
TWO
O
Triangle Wave Output
4
DCA1
I
Duty Adjustment Input 1
5
DCA2
I
Duty Adjustment Input 2
6
(+) Vcc
7
FM
I
Frequency Modulation
8
FS
I
Frequency Sweep
9
SQO
O
Square Wave Output
10
TC
I
Timing Capacitor Input
11
Vee
12
SA2
13
N.C.
No Connection
14
N.C.
No Connection
Positive Power Supply
Negative Power Supply
I
Adjust Sine Waveform Input 2
NTE864 Integrated Precision Circuit Waveform Data for Triangle Wave with reference to
Intersil ICL8038 Precision Waveform Generator [13], [14]
43
Texas Instruments TLE2072 Excalibur Low-Noise High Speed Dual Op Amp [16]
Texas Instruments LM339 Low Power Offset Voltage Quad Comparator [17]
44
Vishay 6N136 High Speed Octocoupler [19]
Microchip Technology Inc. TC1426CPA Inverting MOSFET Driver [20]
Microchip Technology Inc. TC1427CPA Non-Inverting MOSFET Driver [20]
45
International Rectifier IRFP140NPbF HEXFET Power MOSFET [21]
46
Appendix B: Gantt Chart
FALL 2012 (EE460)
Unipolar PWM DC-to-AC- INVERTER PROJECT
Week
Project Plan
1
2
3
4
5
6
7
HOLIDAY BREAK
8
9
10
1
2
3
WINTER 2013(EE463)
4
Abstract (Proposal) V1
Requirements and Specifications
Block Diagram
Literature search
Gantt Chart
Cost Estimates
PWM Inverter Project Analysis
Requirements and Specifications V2
Rough Draft Report
Report V2
Research Power Inverter (DC-to-AC)
Ordering/Inventory of Components
PWM Power Inverter Applications
Firing Circuit
Control Circuit
H-Inverter
Contruction & Testing
Finalize Circuit Layout
Construct and Test Device
If Version I fails to work, then..
Contruction & Testing (version II)
Re-Design/Analysis
Simulation & Sensitivity Analysis
Purchase New Components
Contruction & Testing
Construct and Test Device
Finalize Results and Prepare Data
Interim Report
Final Senior Project Report
Rough Draft
Advisor Review
Second Rought Draft
Advisor Review
Final Senior Project Report
47
5
1
2
3
4
5
6
7
SPRING 2013(EE464)
8
9
10
1
2
3
4
5
6
7
8
9
10
Appendix C: Parts List
Control Circuit
• NTE864, Waveform Generator ,14 – pins (1)
• TLE2072CP, Dual Op Amp, 8 – pins (1)
• LM393N, Quad Comparator, 14 – pins (1)
• NMH1212SC, 2W Dual Output DC-DC Converter (1)
• 16nF, ceramic capacitor (1)
• 0.01uF, ceramic capacitor (1)
• 1kΩ, ¼ W resistor (4)
• 100kΩ, ¼ W resistor (1)
• 10kΩ, ¼ W resistor (1)
• 9.53kΩ, ¼ W resistor (1)
• 270kΩ, ¼ W resistor (2)
• 1.5kΩ, ½ W resistor (2)
• 500Ω ½ W Bourns trimmer (1)
• 1kΩ ½ W Bourns trimmer (1)
• 500Ω, 24 mm Potentiometer (1)
Firing Circuit
• 6N136, Optocouplers (4)
• TC1426, MOSFET Inverting Driver Microchip (2)
• TC1427, MOSFET Non-Inverting Driver Microchip (2)
• NKE0505S, 1 W Dual Output DC-DC Converter (2)
• D0-35 Case, 75V 150mA, High-Speed Switching Diode (4)
• 0.1uF, ceramic capacitor (4)
• 10kΩ, ¼ W resistor (4)
• 10Ω, ¼ W resistor (4)
• 1.2kΩ, ¼ W resistor (4)
• 100kΩ, ¼ W resistor (4)
H-Bridge
• IRFP140N, 100V 33A, N-Channel Power MOSFET (4)
• TO-218, Heat Sink Case (4)
• 10uF, 50V High Frequency Bipolar Capacitors (2)
• 100uH, 10A Inductor (1)
• 10A, 10V Fast – Acting Fuses (2)
• 10A, 250VAC, Chasis- Type ¼” x ¼” Fuse Holder (2)
Other
#
• Proto board – p qrst u v $ qrst (1)
• 14 – pin DIP sockets (2)
• 8 – pin DIP sockets (9)
48
•
•
•
24 – pin SIP socket (1)
Plexiglass Board & Box Cover (1)
Computer Board Standoffs (4)
Cost Estimation
Item
NTE864, Waveform
Generator
TLE2072CP, Dual Op
AMP
LM393N, Quad
Comparator
NMH1212SC, DCDC Converter
6N136, Optocoupler
TC1426, MOSFET
Inverting Driver
Microchip
TC1427, MOSFET
Non-Inverting Driver
Microchip
NKE0505S, DC-DC
Converter
DO-35 Case
Switching Diodes
IRFP140N, N-Power
MOSFET
TO-218, Heat Sink
Fast Acting Fuses
Fuse Holders
Capacitors
Resistors
Potentiometer
Inductor
IC Pin Sockets
Trimmers
Cost Per Unit
$50.00
Quantity
1
Total
$50.00
$3.07
1
$3.07
$0.98
1
$0.98
$13.42
1
$13.42
$1.32
$1.24
4
2
$5.28
$2.48
$1.24
2
$2.48
$7.74
2
$15.48
$0.35
4
$1.40
$2.07
4
$8.28
$3.02
4
$12.08
$2.49
$1.25
$0.40
$0.20
$3.00
$10.45
$1.00
$0.98
2
2
8
27
1
1
12
3
$5.00
$2.50
$3.20
$5.40
$3.00
$10.45
$12.00
$2.94
$159.44
Total:
49
Appendix D: References
Books
[1]
Taufik, and Dale Dolan. Introduction to Power Electronics. Cal Poly State University.
San Luis Obispo: 10th Revision, 2012.
[2]
Taufik, and Dale Dolan. Advanced Power Electronics. Cal Poly State University. San
Luis Obispo: 6th Revision, 2013.
[3]
D. Grahame Holmes, Thomas A. Lipo, Pulse Width Modulation for Power Converters,
Hoboken NJ, USA. 2003
[4]
Bin Wu, High-Power Converters and AC Drives, Hoboken NJ, USA. 2006
Reports
[5]
Tran, Kelvin, and Ryan Sidarto. PWM Inverter. Print. San Luis Obispo: California
Polytechnic State University, 20 May 2011.
[6]
EE362L, Power Electronics, PWM Inverter Control Circuit. Print. 20 October 2008.
[7]
EE362L, Power Electronics, Isolated Firing Circuit for H-Bridge Inverter. Print. 27
October 2008.
[8]
EE362L, Power Electronics, H-Bridge Inverter. Print. Print. 20 February 2008.
Internet
[9]
Wikipedia (2012, October 13) Power Inverters http://en.wikipedia.org/Power_inverter
[10]
Energy Home (2013, May 17) Photovoltaic Cells
http://www.energyeducation.tx.gov/renewables/section_3/topics/photovoltaic_cells/f.htm
l
[11]
Consenergy Biotek (2013, May 17) Grid Connected PV Systems
http://www.consenergybiotek.com/grid_connected.html
[12]
Tripp-Lite (2013, May 24) PowerVerter® 375W Ultra-Compact Inverter with 2 Outlets
http://www.tripplite.com/en/products/model.cfm?txtModelID=2552
Datasheets
[13]
NTE Electronics, “NTE864 Integrated Circuit Precision Waveform Generator,” Data
Sheet Rev. N/A, July 2007.
50
[14]
Intersil, “ICL8038 Precision Waveform Generator/Voltage Controlled Oscillator,” Data
Sheet Rev. 2864.4, April 2001.
[15]
Murata Power Solutions, “NMH Series Isolated 2W Dual Output DC/DC Converters,”
Data Sheet Rev. KDC_NMH.E03, 2012.
[16]
Texas Instruments, “TLE2072 Excalibur Low-Noise High-Speed JFET-Input Op-Amp,”
Data Sheet Rev. SLOS181A, March 2000.
[17]
Texas Instruments, “LM339 Low Power Offset Voltage Quad Comparators,” Data Sheet
Rev. DS005706, March 2004.
[18]
Murata Power Solutions, “NKE Series Isolated Sub-Miniature 1W Single Output DC/DC
Converters,” Data Sheet Rev. NDC_NKE.5, 2001.
[19]
Vishay, “6N136 High Speed Optocoupler, 1 MBd, Photodiode with Transistor Output,”
Data Sheet Rev. 1.8, 05 September 2011.
[20]
Microchip Technology Inc. “TC1426/TC1427 1.2A Dual High-Speed MOSFET
Drivers,” Data Sheet Rev. DS21393C, 2 February 2006.
[21]
International Rectifier, “IRFP140NPbF HEXFET Power MOSFET,” Data Sheet Rev.
PD-95711, 2 August 2004
51